Electric fuse



oct. 4,1927. 1,644,626

I R. H. D. BARKLIE ELECTRIC FUSE Filed Jan. 19,4927

' 1mg-f E. j?. arivzw Patented Oct. 4, 1927.

UNITED STATES ROBERT HENRY DOUGLAS BARKLIE, OF PURLEY, ENGLAND.

ELECTRIC FUSE.

Application filed January 19, 1927, Serial No.

This invention consists in improvements in or relating to electric fusescapable of being operated by very small currents such7 for example, ascurrents of milliamperes and less. i

According to the present invention an electric fuse comprises a film ofmetal supported on an insulating backing, the thickness of the filmbeing substantially not greater than one ve-,thousandths of an inch.

The invention further comprises an electric fuse comprisinga film ofmetal which is so thin that it is not self-supporting for the purposerequired and which is mounted on an insulating backing such, forinstance,

as paper.

The metal film may be prepared in any one of many ways and examples ofsome o f the methods Aof manufacturing fuses according to the inventionwill now be described.

In the accompanying drawing the view illustrates one form of holder ormounting for the fuse ofthis invention.v

In its simplest `form arflm .of metal may be `obtained by the knownprocess of beat* y ing as practised in the gold-beaters art. Forinstance, a gold film may be beaten uni til it is of a thickness thatWill obtain when one-thousand square inches of the metal film has a massof one gramme i. e. thickness is approximately three millionths of aninch. A sheet of paper is coated with gum and the gold film prepared asabove is laid on the paper. The composite sheet thus formed is dried andfor this. purpose it may be left Qin Vanoven ata temperature of 110 C.for

approximately twelve hours.

The sheet may be then out into strips of required size. It is found thata sheet having a metal film 2 cms. long and 0.11 cms. 1in width willcarry a current of 30 milliamperes and `will fuse at approximatelymilliamperes. Experiments have shown that ,avfuse having the same lengthbut a Awidth cih-0.2 cms-will carry a current `of 60 milliamperes andwill fuse at 80 milliamperes. Thus, fuses according tothe inventionwillcarryrcurrents the value of which is roughly in proportion tothe Widthof the The lengthofthe filmmay be small say, for example, 0.2cms.andfinvorderto make fuses which will vcarry heavier currents,

162,201, and in Great Britain October 5,1925.

several films of metal may be superimposed on the one paper backing sothat they are employed m parallel; or several fuse lengths as abovedescribed may be y employed in parallel as will be. readily understood.Other metals such as silver and copper can be employed and can bereduced in thickness toV the .required extent by beating; butiof coursethey will not have identical fusing qualities with those of gold.

It may be therefore said that the inven- `tion comprises an electricfuse which consists of a metal film supported on an insulating backing.the. thickness of the film being less than that which can be obtainedlby rolling las films having a thickness of `the order above specifiedcannot be obtained by known commercial processes for rolling metal foil.

According to another method of preparing the fuse a thin layer of `metalis electrolytically deposited on onesurface of a soluble cathode. Forinstance, .gold can be deposited on silver. Thereafter the .cathodeistreated with a solvent that will dissolve the cathode withoutattacking the metal film.

In the specific case mentioned the silver. elec trode can be removed bynitricacid of strength. This may be eected by first depositing the goldon a thin strip of silver which is fioated on the solvent. vAfter thesilver has been dissolved the gold will be left floating on the surfaceof the `solvent yand the gold can then be ldrawn out on the surface of asheet of glass or Celluloid. Alternatively silver can be deposited on anelectrode of aluminium and the latter then be dissolved in caustic sodato leave a film of silver floating on the solvent. y

The upper surface of the ,gold or other metal film can be readily Washedwhile it is von the glass or celluloid surface `from which it has beenremoved from the solvent. In order to wash the undersurface, thetemporarysupport (the glass or celluloid sheet) is dipped into a bath ofwater atsuchean angle that .although .the Vsupport is im* mersedthegoldpor .metralfilm will float off on vto the surface ofthe waterwhich ,will thereby wash the underside thereof. The metal film can beremoved from the Washing Water and be re-Washed in a similar manner asmany times as may be foundnecessary and finally itis Washed similarly inalcohol.

The metal film can then be pulled or lifted from the alcohol washingbath on to a film of paper or other insulating material that is preparedin such a manner that when dried the metal film will adhere closelythereto.

LAccording to a further method of preparing fuses in accordance with thepresent invention, the metal is applied to an insulating backing in afinely divided condition. For instance it may be sprayed under preslsureby well known processes and thereafter consolidated and renderedhomogeneous by mechanical treatment such rolling. The metal may beotherwise applied to the in.- sulating backing in a finely dividedcondition and'subsequently rend-ered homogeneous by rolling. Suchmethods are particularly suitable in the case of metals such as tin,lead', or tin-lead alloys.

Another method consists in sputtering or flashing metal in a finelydivided condition by an ionization process such as a positive raydischarge in vacuo. It is thought unnecessary to describe such processesin detail as they are already-well known and are used, for example, (forother purposes) in flashing a metal such as magnesium in the finaltreatment'for the evacuation of thermionic tubes. f

A still further ymethod consists in boiling a mass of themetal fromwhich the fuse is to be formed in an electric furnace such as a highfrequency induction current furnace. The boiling metal vapour may beconducted on to the surface of an insulating backing and be condensedthereon so as to afford a film of the thickness desired.

As another alternative method a thin lilm of silver may be deposited onto the insulating backing from a silver compound (such as an ammoniacalsolution of silver nitrate) by a chemical reducing agent (such asformaldehyde) as in the known art of forming silver mirrors.

When an'electrolytic method of depositing themetal film is resorted tovas described above a. fine deposit can be obtained and the thickness ofthe film can be reduced consideral processes given above are examplesonlyr of the rvarious methods by which the invention can be carried intoeffect.

A convenient method of mounting fuses made in accordance with thisinvention comprises a clip-having two jaws or gripping l velements 2.

elements spring pressed towards one another or clamped by means of ascrew or other equivalentineans. @ne element is of metal and the otheris of rubber or some other compressible material so that the. fuse isgripped by the metal element against the rubberelenient with the formerincontact with the metal film constituting the fuse.

.Referring now to the drawing, the above referred to mounting isillustrated in the fig ure and wherein the thin fuse layer of `metal isindicated at l. The fuse strip l at each end is held between metalelements or jaws 2 and 3 between which is interposed a strip of rubber4, the strip fi having a portion lying between the metal element 3 andthe insulating backing of the fuse strip l. The metal layer l of thefuse is thus held at each end in contact with the metal element 2.

Each pair of metal elements 2 and 3, to-.

' or other insulating tube which hold the end caps andthe elements 2 and3 therein in spaced apart and insulating relation. The parts 2, 3 and tfit tightly within the ends of the insulatingtube 6, so that the fusestrip l will be gripped firmly between the parts at each end and providea good electrical contact between the strip l and the In assembling thefuse structure, one pair of metal 'elements 2 and 3, and the rubber orlike compressible strip 4, 'may be secured within an end cap 5. lOne endof the stripl may then be gripped between Vthe parts 2 and 4; and theassembly inserted within one end of the tube 6. -From the other end ofthe tube, the metal element A2 and the rubber strip 4; are then insertedso as to retain the end of `the 'fuse strip l between them. Finally, themetal element 3 is forced into the end of the tube and the enel cap 5fitted over the parts.

F or establishing electrical connection with the fuse, the' tubularfuseassembly may be held betweenthe contact springs 7 which are mountedV inthe insulating base 8 provided with binding'posts and nuts y9 for makingelectrical connection Vbetween the springs 7 and the terminals of anexternal electric circuit. `V

I claim gl. Armeth'od of manufacturing an electrie fuse "which consistsin electrically depositing metal on to a soluble electrode so Vthat thethickness of the metal is substantially not greater'than that ofcommercially 'beaten gold, dissolving the electrode from the depositedmetal and thereafter floating the metal iilm on to an insulating backingand removing the solvent from the composite sheet thus formed.

2. A method of manufacturing an electric fuse which consists inelectrically depositing metal on to a soluble electrode so that thethickness of the metal is substantially not greater than that ofcommercially beaten gold, dissolving the electrode from the depositedmetal2 floating the metal-film on a substantially rigid support andremoving it thereby from the electrolyte, and thereafter, as often asmay be required, immersing the support in a Washing liquid in sucli amanner that the film floats ofi' on to the Washing liquid so that itsunderside is Washed clear of electrolyte and subsequently floating thefilm on to al permanent insulating backing.

3. A method of manufacturing an elec-` tric fuse which consists indepositing metal on to a soluble support, thereafter dissolving saidsupport and recovering the metal film on a backing.

4. A method of manufacturing an electric fuse which consists indepositing metal on to a support by a process whereby the thickness ofthe deposited metal film gradually grows, removing said metal film on to4the surface of a liquid and subsequently recovering the film from theliquid on to a backm0'.

n testimony whereof I affix my signature.

ROBERT HENRY DOUGLAS BARKLIE.

